Diversity of late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America

The tooth taxon Aublysodon mirandus was reinstated following the collection of nondenticulate tyrannosaurid premaxillary teeth from late Maastrichtian deposits in western North America. A small skull from the Hell Creek Formation of Montana (the ‘Jordan theropod’, LACM 28471), that was associated with a nondenticulate premaxillary tooth, was referred to Aublysodon and the diagnosis was revised to include cranial bones. However, the ‘premaxillary’ tooth of the specimen is actually a maxillary tooth. The small size of Aublysodon crowns, and evidence that some denticles develop late in growth in theropods, indicates that the nondenticulate condition represents immaturity. Therefore, Aublysodon is a nomen dubium. The Jordan theropod was recently designated as the type specimen of Stygivenator molnari . A tyrannosaurid from the Hell Creek Formation of Montana (LACM 23845) was first referred to Albertosaurus cf. A. lancensis and then later became the type specimen of Dinotyrannus megagracilis . On the basis of shared derived characters and a quantitative reconstruction of the growth series of Tyrannosaurus rex , the type specimens of S. molnari and D. megagracilis are juvenile and subadult specimens of T. rex , respectively. There is currently  evidence  for  only  one  tyrannosaurid  species  in  the  late  Maastrichtian  of  western  North  America:  T. rex . © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 142 , 479–523.